Nato's intensified aerial bombardment of Tripoli continued early on Wednesday, hours after Libyan leader Muammar Gaddafi made a rare speech on state television vowing to fight to the death.

Loud explosions rocked the city before dawn, marking the heaviest 24 hours of air strikes in the capital since Nato's operation began in March. The alliance said it conducted 66 strike sorties on Tuesday, with many of them in daylight hours. Previously, most airstrikes have taken place at night.

The targets struck in and around Tripoli included six command and control centres, two anti-aircraft guns, a radar system and a vehicle storage facility, according to Nato. The heaviest damage occurred at Gaddafi's Bab al-Aziziya compound, where several buildings were destroyed, sending giant plumes of smoke into the sky.

Gaddafi, who is in hiding in the capital and has rarely been seen or heard from in recent weeks, reacted with fury to the attack. In a nine-minute audio clip broadcast on state television, he said: "We will not surrender: we only have one choice to the end. Death, victory, it does not matter, we are not surrendering."

Government spokesman Moussa Ibrahim later said that 31 people – soldiers, guards, and civilians – had been killed in Tuesday's bombing raids, and described Nato as "the forces of evil". The casualty figure could not be independently verified.

In an attempt to show that Nato had struck non-military targets, government minders on Wednesday morning took journalists to see a "nature reserve", occasionally used by Gaddafi to entertain guests, that had been hit the previous evening.

The missiles had destroyed two trucks, one of them very large, a golf cart, a large tent and several containers, including one that had computer equipment and a paper shredder inside. Local officials were unable to explain what the vehicles were doing on a nature reserve, or why there were several windsocks nearby, which appeared to suggest the presence of an airfield.

The surge in the number of attacks on targets in Tripoli, which follows the incorporation of attack helicopters into Nato's mission at the weekend, is a clear attempt to end the military stalemate on the ground and hasten Gaddafi's exit. Nearly four months into the conflict, rebels control large parts of eastern Libya, the coastal city of Misrata, and a string of towns in the western mountains, near the border with Tunisia. But the rebels, described as "bastards" in Gaddafi's television broadcast, are making very slow progress towards Tripoli, where the regime still has a tight grip on the population.

Nato defence ministers are holding a meeting in Brussels on Wednesday at which the alliance's secretary general, Anders Fogh Rasmussen, will push for broader involvement from the allies in the escalating operation. Britain and France are currently leading the military mission.

The US president, Barack Obama, said on Tuesday that the operation was progressing well, and that it was "just a matter of time before Gaddafi goes".

If he does, it seems increasingly unlikely it will be peacefully. Ibrahim said on Tuesday night that the west had not given the regime a chance to enter into negotiations, and said an African Union "roadmap" to peace was the best way forward. But he insisted that there could be no preconditions – alluding to suggestions that Gaddafi leave power and go into exile.

And while the government spokesman repeated the claim that the war was an attempt by the west to take revenge on Gaddafi for his past ills and seize the country's oil, others in the regime continue to raise the Islamist bogeyman.

In comments broadcast on state television last night, one of Gaddafi's sons, the former professional footballer Saadi, said: "[Muslim] Brotherhood members, jihadists and takfiris (other Islamist fundamentalists) should not dream to return to Libya to take charge of it. This is a battle of principles. The leader and the Libyan people have nothing to do with it."